Link plate for a silent chain

ABSTRACT

A link plate for silent chains  10  includes a pair of teeth or toes  10   a  each formed of an inside flank  11  and an outside flank  12  and a pair of pin apertures  10   b  to insert connecting pins  3  thereinto. A moment M around a pin  3  is shown as follows: M=F×Lo where F is a force applied by a tooth  21  of a sprocket  20  against a meshing point  12   e  on the outside flank  12,  and Lo is a length of a perpendicular drawn from a center O of a pin aperture  10   b  to an action line m of the force F. In order to decrease this moment M, the length Lo of the perpendicular is shortened, said link plate having an engaging point E with a tooth of a sprocket on an intersection between a straight line n and a flank, said straight line n and the direction of a central line connecting each center O of pin apertures forming a pressure angle α, and being in contact with a circle C, said circle C having a center located at a center O of said pin aperture and a radius r≦0.25×P, where P is a pin aperture pitch. Also, a pressure angle α of the outside flank is determined to satisfy an inequality, 32°≦α≦34°, to lessen the force F.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a link plate for a silent chain,and more particularly, to an improvement of structure to decrease noiseof the silent chain during operation.

[0003] 2. Description of Related Art

[0004] A silent chain is generally constructed from a plurality of linkplates each having a pair of teeth and pin apertures and arranged inlateral and longitudinal directions and joined pivotably by connectingpins.

[0005] There are various frequencies in noise that occurs duringoperation of a silent chain. In these frequencies, a frequency havingthe greatest intensity forms a so-called primary oscillation ofengagement. Since such primary oscillation of engagement givesobjectionable impression to ears of human beings, various efforts andimprovements have been made to decrease the primary oscillation ofengagement.

[0006] Referring to FIG. 6, the around-the-pin moment will be explained.FIG. 6 shows a state of engagement of a link plate in a specified row ofa silent chain with a sprocket teeth. A link plate 100 is engaged with asprocket 200 rotating in an arrow mark direction. The link plate 100includes a pair of teeth 110 and pin apertures 120 having pins 130inserted thereinto. Each of the teeth 110 is formed of an inside flank111 and an outside flank 112. A tooth 210 of the sprocket 200 is incontact with the outside flank 112 of one of the teeth 110 of the linkplate 100.

[0007] In such a state of engagement, tension T is applied to each rowof link plates forming a silent chain. On the other hand, force F fromthe sprocket tooth 210 is applied to an engagement point 112 e on theoutside flank 112 of the link plate 100. When a length of aperpendicular drawn from a center of a pin aperture to an action line ofthe force F is L, a moment M around a pin is shown by M=F×L.

SUMMARY OF THE INVENTION

[0008] A link plate of a silent chain according to the present inventionhas a pair of teeth each formed of an inside flank and an outside flank,and a pair of pin apertures to insert connecting pins. As shown in FIG.2, the link plate has an engaging point E engaged with a sprocket toothon an intersection between a straight line n and a flank. The straightline n is at an angle α(α: pressure angle of a flank) with the directionof a central line connecting each center O of pin apertures and incontact with a circle C. The circle C has a center located at a center Oof the pin aperture and a radius r, which is equal to or smaller than0.25×P (P: pin aperture pitch or distance between centers of pinapertures).

[0009] As is seen from FIG. 2, the straight line n corresponds to anaction line of force F applied from the sprocket tooth to the engagingpoint E of the link plate. The radius r of the circle C corresponds to alength of a perpendicular drawn from the center O of the pin aperture tothe action line of the force F at the engaging point E. Also, the radiusr satisfies an inequality, r≦0.25×P (as opposed to a prior art linkplate, in which there was an inequality, r>0.25×P), and the radius r issmall. Thus, around-the-pin moment M (=F×r) is relatively small, therebydecreasing primary oscillation of engagement. Moreover, in the presentinvention, an arm length of around-the-pin moment can be shortenedirrespective of the size of the pressure angle α of the flank.Preferably, the pressure angle α of the flank satisfies an inequality,α>30°.

[0010] The connecting pin may be a round, cylindrical pin of a roundsectional shape. Alternatively, the connecting pin may be a rocker jointformed of a rocker pin and a joint pin. In a rocker joint type silentchain, an intersecting point O′ (not shown) between a rocker pin and ajoint pin with the silent chain linearly extended corresponds to acenter O of the pin aperture for a round pin. In the case of a rockerjoint type silent chain as well, the arm length of around-the-pin momentcan be shortened regardless of the size of the pressure angle α of theflank. Thus, around-the-pin moment can be made relatively small, therebydecreasing primary oscillation sound of engagement.

[0011] Therefore, from a viewpoint of lessening the around-the-pinmoment and preventing tooth jumping of a sprocket tooth, the pressureangle α, more preferably, satisfies an inequality, 32°≦α<34°. In thiscase, not only an arm length of the moment but also a component of aforce constituting the moment can be lessened, thereby furtherdecreasing around-the-pin moment, thus further reducing primaryoscillation sound.

BRIEF DESCRIPTION OF THE DRAWING

[0012] For a more complete understanding of the invention, referenceshould be made to the embodiments illustrated in greater detail in theaccompanying drawings and described below by way of examples of theinvention. In the drawings, which are not to scale:

[0013]FIG. 1 is a front elevational view of a portion of a silent chaintransmission device according to an embodiment of the present invention,showing a link plate of a silent chain in engagement with acorresponding sprocket.

[0014]FIG. 2 is a front elevational view of a link plate of FIG. 1,illustrating an engaging point of a link plate with a sprocket tooth.

[0015]FIG. 3A is a front view of a link plate having a flank pressureangle α1, showing forces applied to the link plate.

[0016]FIG. 3B is a front view of a link plate having a applied pressureangle α2, showing forces applied to the link plate.

[0017]FIG. 4A shows a triangle of forces applied to the link plate ofFIG. 3A having a flank pressure angle α1.

[0018]FIG. 4B shows a triangle of forces applied to the link plate ofFIG. 3B having a flank pressure angle α2.

[0019]FIG. 4C shows a combination of FIGS. 4A and 4B.

[0020]FIG. 5 is a graph showing the result of a noise test of a silentchain transmission device according to the present invention.

[0021]FIG. 6 is a front elevational view of a portion of a prior artsilent chain transmission device, showing a link plate of a silent chainin engagement with a corresponding sprocket.

[0022]FIG. 7 is a graph showing the result of a noise test of a priorart silent chain transmission device.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Moment of a force around a connecting pin (hereinafter called“around-the-pin moment”) that is applied to an engagement surface of alink plate at the time of meshing with a sprocket tooth greatlyinfluences the primary oscillation of engagement. According to theteachings of this invention, when around-the-pin moment M becomesgreater, fluctuation in tension easily occurs, and such torquefluctuation occurs synchronized with engaging frequency, thereby causingprimary oscillation of engagement, which transmits to a peripheraldevice and becomes a source of engaging sound. Therefore, primaryoscillation sound will be decreased by decreasing around-the-pin moment.

[0024] Referring now to the drawings, FIG. 1 shows a portion of a silentchain having a plurality of rows of link plates provided along thelength of the chain, illustrating a link plate of a specified rowengaging with a sprocket. As shown in FIG. 1, a link plate 10 includes apair of teeth 10 a and pin apertures 10 b. Each of the teeth 10 a isformed of an inside flank 11 and an outside flank 12. In each of theapertures 10 b is inserted a round, cylindrical connecting pin of around sectional shape adapted to pivotably connect adjacent rows of linkplates. At a point 12 e on the outside flank 12, the link plate 10 is inengagement with the teeth 21 of the sprocket 20 rotating in thedirection of an arrow mark.

[0025] In such an engagement state, tension T is applied to the link rowincluding the link plate 10. A compressive force F is applied from thesprocket tooth 21 to the engagement point 12 e on the outside flank 12of the link plate 10. At this time, around-the-pin moment M is definedby the equation, M=F×Lo, wherein Lo is a length of a perpendicular drawnfrom a center O of a pin aperture 10 b to an action line m of the forceF.

[0026] The position of the engagement point of the link plate 10 will beexplained using FIG. 2, which shows a link plate of FIG. 1. In FIG. 2,first, a circle C is drawn, with its center located at the center O of apin aperture and a radius r, which is equal to or smaller than 0.25×P(where P is the pin aperture pitch or distance between the centers ofthe pin apertures). Then, a straight line n is drawn that is at an angleα (where a is the flank pressure angle) with the direction of a centerline connecting each center O of the pin apertures and that is tangentto the circle C. An intersection E between the straight line n and theoutside flank 12 will be an engaging or mating point with a sprockettooth.

[0027] As is seen from FIG. 2, the straight line n corresponds to anaction line of the force F (or the action line m of FIG. 1) applied tothe engaging point E on the link plate from the sprocket tooth. Theradius r of the circle C corresponds to a length of the perpendicular(or Lo of FIG. 1) drawn from the center O of the pin aperture to theaction line of the force F at the engaging point E. Also, the radius rsatisfies r<0.25×P, and r is relatively small. Thus, around-the-pinmoment M (=F×r) is relatively small, thereby decreasing primaryoscillation sound. Moreover, in this case, the arm length of thearound-the-pin moment can be lessened irrespective of the size of theflank pressure angle α.

[0028]FIG. 3A shows a link plate having a flank pressure angle of 30degrees or less, and FIG. 3B shows a link plate having a flank pressureangle more than 30 degrees. In the drawings, the angle α₁ for the linkplate 30 is 30°, and the angle α2 for the link plate 40 is 32°.

[0029] To the link plate 30 are apllied a chain tension T, a compressiveforce F₁ from the sprocket tooth at the engaging point of the flank, anda tensile force W₁ from the link plate adjacent to the link plate 30.These forces T, F₁ and W₁ are balanced. The tensile force W₁ is at anangle O with the direction along the center line of the pin apertures.

[0030] To the link plate 40 are applied a chain tension T, a compressiveforce F₂ from the sprocket tooth at the engaging point of the flank,arid a tensile force W₂ from the link plate adjacent to the link plate40. These forces T, F₂ and W₂ are balanced. The tensile force W₂ is atan angle θ with the direction along the center line of the pinapertures.

[0031]FIG. 4A shows a triangle of forces for the link plate 30 and FIG.4B shows a triangle of forces for the link plate 40. FIG. 4C shows acombination of FIGS. 4A and 4B. In FIG. 4C, the pressure angle α2 isexaggerated for the purpose of illustration.

[0032] As is clearly seen from FIG. 4C, for the compressive forces F₁and F₂, an inequality, F₂<F₁ is satisfied. In other words, thecompressive force applied from the sprocket tooth becomes smaller whenthe pressure angle becomes greater than 30 degrees. Thus, around-the-pinmoment can be made relatively smaller, thereby reducing primaryoscillation sound of engagement.

[0033] The flank pressure angle α preferably satisfies a >30°. Thereason for this is that in the case of a pressure angle greater than 30degrees, as above-mentioned, a compressive force acting from thesprocket tooth becomes smaller, thus making the around-the-pin momentrelatively smaller, thereby decreasing primary oscillation sound.

[0034] Also, the flank pressure angle α preferably satisfies a <34°. Thereason for this is that in the case of the pressure angle of 34 degreesor more, the tilting angle of the flank that is declined from thedirection of the radius of the sprocket becomes greater, thereby causingthe tooth jumping of the sprocket. Moreover, the pressure angle α morepreferably satisfies a ≧32°.

[0035] Therefore, from the standpoint of lessening the around-the-pinmoment and preventing the tooth jumping of the sprocket, the pressureangle α more preferably satisfies 32°≦α≦34°. In this case, since the armlength of the moment can be made smaller and the component of the forceconstituting the moment can be lessened, the around-the-pin moment isfurther decreased and primary oscillation sound is further reduced.

[0036]FIG. 5 shows the result of the noise test of a silent chaintransmission device according to the preferred embodiment of the presentinvention. In this test, the pressure angle of the outside flank of thelink plate is 32.7°, and the pressure angle of the sprocket tooth, orthe pressure angle at the engaging point with the outside flank of thelink plate, is also 32.7°. The arm length of the around-the pin momentis 0.23×P (where P is the pin aperture pitch). In FIG. 5, a rotationalspeed in a horizontal axis shows a rotating speed of a drive sprocket(and also a driven sprocket) of a test equipment, and a vibration oroscillation in a vertical axis shows a measured value measured by anoise meter at each rotating speed. Graph line (1) shows an overallsound representing oscillation of the whole device, and graph line (2)shows a primary oscillation sound.

[0037] In FIG. 5, an evaluation point is at the rotating speed of 2,450rpm where the highest oscillation is measured. The primary oscillationat this evaluation point is 72 dB.

[0038] On the other hand, FIG. 7 shows the result of the noise test of aprior art silent chain transmission device. In this test, the pressureangle of the outside flank of the link plate is 30°, and the pressureangle of the sprocket tooth is 32.7°. The arm length of thearound-the-pin moment is 0.35×P. The other conditions are the same asthose of the noise test in FIG. 5.

[0039] In FIG. 7, an evaluation point is at the rotating speed of 2,675rpm where the highest oscillation is measured. The primary oscillationat this evaluation point is 84 dB.

[0040] In comparison between FIGS. 5 and 7, according to the embodimentof the present invention, the primary oscillation decreases 12 dB.

[0041] In the above-mentioned preferred embodiment, there is shown anexample where the outside flank pressure angle α satisfies 32°≦α≦34° andthe arm length of the around-the-pin moment is lessened, but the presentinvention is not limited to this example.

[0042] The pressure angle α satisfying 32°≦α≦34° can solely lessen thecomponent of the force constituting the around-the-pin moment, therebydecreasing the moment and thus, reducing the primary oscillation sound.Alternatively, the shortened arm length of the around-the-pin moment cansolely decrease the around-the-pin moment, thereby reducing the primaryoscillation sound.

[0043] Also, the preferred embodiment describes the pressure angle ofthe outside flank only, but for the link plate engaging with thesprocket tooth at the inside flank, the pressure angle at the insideflank should be considered.

[0044] Furthermore, the present invention can be applied to a rockerjoint type silent chain having a plurality of sets of a rocker pin and ajoint pin. In this case, the intersection O′ (not shown) between therocker pin and the joint pin with the silent chain linearly extendedcorresponds to the center O of the pin aperture of the link plate in thepreferred embodiment. In this case as well, similarly to the preferredembodiment, the arm length of the around-the-pin moment can be lessenedirrespective of the size of the flank pressure angle α, thus decreasingthe around-the-pin moment, thereby reducing the primary oscillationsound. Also as with the preferred embodiment, by suitably predeterminingthe pressure angle α, the component of the force forming the moment canbe lessened and the around-the-pin moment can be decreased, therebyreducing the primary oscillation sound, and the tooth jumping of thesprocket can be prevented.

[0045] Those skilled in the art to which the invention pertains may makemodifications and other embodiments employing the principles of thisinvention without departing from its spirit or essential characteristicsparticularly upon considering the foregoing teachings. The describedembodiments and examples are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. Consequently, while the invention has been described withreference to particular embodiments and examples, modifications ofstructure, sequence, materials and the like would be apparent to thoseskilled in the art, yet fall within the scope of the invention.

What is claimed is:
 1. A link plate for a silent chain, in which aplurality of said link plates are arranged in lateral and longitudinaldirections and joined pivotably by connecting pins, said link platehaving a pair of teeth each formed of an inside flank and an outsideflank and a pair of pin apertures to insert said connecting pinsthereinto, said link plate having an engaging point E with a tooth of asprocket on an intersection between a straight line n and a flank, saidstraight line n and the direction of a central line connecting eachcenter O of pin apertures forming a pressure angle α, and being incontact with a circle C, said circle C having a center located at acenter O of said pin aperture and a radius r≦0.25×P, where P is a pinaperture pitch.
 2. The link plate of claim 1, in which the connectingpins are round pins, and P is the distance between centers of said pairof pin apertures.
 3. The link plate of claim 1, in which the connectingpins are a rocker pin and a joint pin, and P is a distance betweencontact points of said rocker pin and said joint pin when said chain ispulled straight.
 4. The link plate of claim 1, wherein said pressureangle α satisfies an inequality, α>30°.
 5. The link plate of claim 4,wherein said pressure angle α satisfies an inequality, α<34°.
 6. Thelink plate of claim 1, wherein said pressure angle α satisfies aninequality, 32°≦α<34°.
 7. A link plate for a silent chain, in which aplurality of said link plates are arranged in lateral and longitudinaldirections and joined pivotably by connecting pins, said link platehaving a pair of teeth each formed of an inside flank and an outsideflank and a pair of pin apertures to insert said connecting pinsthereinto, in which a pressure angle α of said inside flank or saidoutside flank satisfies an inequality, 32°≦α<34°.
 8. The link plate ofclaim 7, in which said link plate having an engaging point E with atooth of a sprocket on an intersection between a straight line n and aflank, said straight line n and the direction of a central lineconnecting each center O of pin apertures forming a pressure angle α,and being in contact with a circle C, said circle C having a centerlocated at a center O of said pin aperture and a radius r≦0.25×P, whereP is a pin aperture pitch.
 9. A silent chain formed of a plurality oflink plates arranged in lateral and longitudinal directions and joinedpivotably by connecting pins, each link plate having a pair of teetheach formed of an inside flank and an outside flank and a pair of pinapertures to insert said connecting pins thereinto, said link platehaving an engaging point E with a tooth of a sprocket on an intersectionbetween a straight line n and a flank, said straight line n and thedirection of a central line connecting each center O of pin aperturesforming a pressure angle α, and being in contact with a circle C, saidcircle C having a center located at a center O of said pin aperture anda radius r≦0.25×P, where P is a pin aperture pitch.
 10. The chain ofclaim 9, in which the connecting pins are round pins, and P is thedistance between centers of said pair of pin apertures.
 11. The chain ofclaim 9, in which the connecting pins are a rocker pin and a joint pin,and P is a distance between contact points of said rocker pin and saidjoint pin when said chain is pulled straight.
 12. The chain of claim 1,wherein said pressure angle α satisfies an inequality, 32°≦α<34°.
 13. Asilent chain formed of a plurality of link plates are arranged inlateral and longitudinal directions and joined pivotably by connectingpins, said link plate having a pair of teeth each formed of an insideflank and an outside flank and a pair of pin apertures to insert saidconnecting pins thereinto, in which a pressure angle α of said insideflank or said outside flank satisfies an inequality, 32°≦α<34°.
 14. Thechain of claim 13, in which said link plate having an engaging point Ewith a tooth of a sprocket on an intersection between a straight line nand a flank, said straight line n and the direction of a central lineconnecting each center O of pin apertures forming a pressure angle α,and being in contact with a circle C, said circle C having a centerlocated at a center O of said pin aperture and a radius r≦0.25×P, whereP is a pin aperture pitch.